The present invention relates generally to wood processing apparatus, and particularly to a wood chipping knife and associated mounting assembly.
A chipper is a wood processing apparatus reducing wood products or parts thereof to small articles referred to herein as "chips." Chips may be produced by reducing completely a given wood article, e.g., an entire log, or may be produced in the context of surfacing a wood article, e.g., establishing a planar surface of a log to be further processed such as by sawing.
Chips produced are useful byproducts. For example, chips are often used in fiber based products such as paper. Important characteristics of the chips produced, and establishing a value therefor, relate to quality and ease of use in producing other products. For example, chips are desirably of uniform size when applied to paper making process to make consistent the paper manufacturing process of breaking down the chips into a wood pulp. More particularly, uniform chip thickness insures that the step of "cooking" the wood chips for reduction to wood pulp can occur under consistent operating conditions. Accordingly, an important characteristic of a chipper is an ability to produce chips of consistent dimension.
A chipper generally comprises a disc structure rotating at high speed and carrying thereon a set of chipper knives. The subject matter of the present invention relates to such chipper knives and the related mounting assembly therefor. Chips are abrasive material, especially when presented to the high speed rotating chipper knives. Chipper knives and associated support structures undergo tremendous stress and wear during operation. Accordingly, chipper knives and related support structures must endure such abrasive conditions for as long as possible while still producing acceptable output, i.e., while still producing consistently dimensioned chips.
Each chipper knife includes a cutting edge and, given that a plurality of such knives work in unison, each chipper knife edge must be carefully aligned or calibrated in its mounting structure to define a common cutting plane for a given set of knife edges. In this manner, the chipper presents to an oncoming wood article a single cutting plane and as the wood article feeds into the chipper knives consistently dimensioned chips result.
A traditional "bent-knife" chipper arrangement carries on the rotating disc structure a plurality of chipper knives each of unitary construction, but presenting two cutting edges angled relative to one another. One cutting edge provides a hogging function while the other cutting edge provides a planing function. Elaborate mounting and maintenance methods and apparatus have been developed for such unitary "bent-knife" chipping systems. A more recent trend, however, has been use of dual-knife systems wherein a pair of straight edge chipping knives mounted adjacent one another in angled relation serve as a replacement for the complex and difficult to maintain unitary "bent-knife" chipping arrangements.
Thus, chipper maintenance can require a relatively high degree of expertise when mounting, dismounting, and maintaining chipper knives. Unfortunately, such expertise can be a limited resource in many wood processing installations. Furthermore, the task of and equipment required for grinding a unitary "bent-knife" is both time consuming and expensive. Any time a unitary "bent-knife" is dismounted for resurfacing, the processing of remounting within the chipper head requires babbiting and precision adjustment to establish the desired cutting plane.
Generally, dual-knife systems have as an objective a simplified registration scheme for the knife blades, i.e., simplified relative to the unitary "bent-knife" chipping systems. Also, these dual-knife systems seek to reduce the level of expertise required in dismounting and remounting chipper knives. In many cases, the chipper knives have two cutting edges, and the knives are "reversible" whereby a single knife may be dismounted, reoriented, and remounted to present a new cutting edge. As may be appreciated, in executing such dismounting and remounting of knives, the resulting configuration must still present a unified cutting plane to the oncoming wood article to maintain consistent the chip output.
U.S. Pat. No. 5,271,440 issued Dec. 21, 1993 to Joseph R. Bradstreet, Jr., et al, and entitled CHIPPER DISC ASSEMBLY HAVING EXTENDED-LIFE REGRINDABLE DISPOSABLE KNIVES shows a chipper knife assembly for a disc type wood chipper including a reversible and disposable knife with a serrated surface. The serrated surface provides predetermined registration of the knife relative to a mounting assembly whereby disc mounting and remounting of the knife requires little or no precision calibration to establish the desired cutting plane among a plurality of such knives. The chipper knife can be thereby dismounted and reground and, when remounted, advanced along the serrated clamping surface to maintain a desired edge position, i.e., to establish the desired cutting plane.
U.S. Pat. Nos. 4,771,718; 4,850,408; 4,997,018; and 5,271,442 issued Sep. 20, 1988; Jul. 25, 1989; Mar. 5, 1991; and Dec. 21, 1993 to Charles T. Carpenter and Robert M. Bailey show various forms and progressive development of a chipper disc and knife assembly including a registrable mounting structure and a reversible knife, i.e., a knife having two cutting edges with the advantage of reversibility and extending the useful life of each knife between reconditioning, i.e., honing, thereof.
The chipper knife bears by far the majority of stress and wear against the abrasive wood product. The supporting structure, however, must also necessarily be exposed to the abrasive wood product. In particular, an inclined surface of the support structure adjacent the cutting edge of the chipper knife, referred to as the "chip breaker", carries the chip away from the chipper knife and completes the task of breaking the chip into desired thickness. Accordingly, the chip breaker is necessarily exposed to the abrasive wood product, and constitutes in all known chipper systems a wear element. Typically, the chip breaker is provided as a leading face of a clamp plate holding the knife in place. Because this chip breaker is an important aspect of consistent chip size, its wear during operation represents a source of degradation in chip quality. Accordingly, the clamp plate comprising the chip breaker must be periodically replaced to maintain chip consistency.
The subject matter of the present invention addresses the above concerns in chipper knife construction and associated supporting structure.